A preliminary report released Thursday by the National Transportation Safety Bureau determined that a self-driving Volvo equipped with Uber's self-driving sensors spotted a pedestrian roughly 6 seconds before it struck and killed her, but didn't attempt to stop because the automatic braking feature was disabled in self-driving mode.

The report said that the Uber safety driver, Rafaela Vasquez, only spotted the pedestrian, Elaine Herzberg, less than a second before the fatal impact and didn't brake until less than a second after the collision.

Investigators said that the self-driving Volvo XC90 equipped with Uber's sensors, cameras, and lidar that Vasquez was driving that night had automatic emergency braking, but it wasn't activated in the minutes leading up to the crash. The report said that automatic braking was disabled in the Uber self-driving cars in autonomous modes "to reduce the potential for erratic vehicle behavior."

According to the report, Uber's self-driving systems deactivated automatic emergency braking and relied on human safety drivers to intervene to avoid a crash. Uber's systems did not alert drivers to take control.

When the Uber self-driving cars operate in "manual mode," with a human driver behind the wheel, the cars use Volvo's standard safety systems, including forward-collision warnings with automatic emergency braking, the report said.

Data from the self-driving systems show the car's radar and lidar systems "saw" Herzberg roughly 6 seconds before the crash or more than 350 feet away from the vehicle, which was traveling at 43 mph. The system first determined that Herzberg was an unknown object, then as a vehicle, then as a bicycle with varying travel paths.

According to the report, the Uber sensors determined that 1.3 seconds before the crash that an emergency maneuver would be necessary.

At roughly 40 mph or about 63 feet per second, the Volvo would have needed more than 80 feet to brake to a stop. Volvo has said that its systems can begin braking in less than a second, and that human drivers would need more than one second to start themselves.

The report outlines the parts of the night leading up to the crash. Vasquez left the Uber garage at 9:14 p.m. and drove a usual test loop in the XC90. She initiated the self-driving mode at 9:39 p.m. until the crash at 9:58 p.m.

In videos released after the crash, Vasquez is seen looking away from the road several times before the crash. Vasquez told officials that she had both work and personal cellphones in the vehicle, but did not use them until after the crash, when she dialed 911.

Vasquez said she was monitoring diagnostic information from the self-driving car, which Uber required of its drivers.

Shortly after the crash, Arizona Governor Doug Ducey suspended Uber's permits to test self-driving cars in the state. On Wednesday, Uber announced it would halt testing in Arizona and continue tests in Pittsburgh and California for the self-driving cars.

In a statement emailed to Motor Authority, Uber said it would cooperate with investigators.

“Over the course of the last two months, we’ve worked closely with the NTSB. As their investigation continues, we’ve initiated our own safety review of our self-driving vehicles program. We’ve also brought on former NTSB Chair Christopher Hart to advise us on our overall safety culture, and we look forward to sharing more on the changes we’ll make in the coming weeks,” an Uber official said in a statement.